INVOICE_ID – NUMBER : Unique internal Identifier for this record. Generated using a database sequence.
VENDOR_ID – NUMBER  : The unique internal identifier of the supplier to which the invoice belongs. Foreign key to the AP_SUPPLIERS table.
INVOICE_NUM : Invoice number for an invoice. This number entered will be unique per supplier and operating unit.
SET_OF_BOOKS_ID : Ledger unique identifier
INVOICE_CURRENCY_CODE : Currency code of the invoice. Foreign key to the FND_CURRENCIES table.
PAYMENT_CURRENCY_CODE : Currency code of payment. If the Invoice Currency is not a fixed-rate currency, then the Payment Currency will be the same as the INVOICE_CURRENCY_CODE. For fixed-rate currency such as euro or another EMU currency it can be different to  INVOICE_CURRENCY_CODE
PAYMENT_CROSS_RATE NUMBER : Yes Exchange rate between invoice and payment. The value is always 1 unless they are associated fixed-rate currencies such as euro or another EMU currency.
DOC_SEQUENCE_ID NUMBER :  Unique Sequence identifier assigned to an invoice, based on the document category of the invoice. Foreign key to the DOC_SEQUENCE_ID of the AP_DOC_SEQUENCE_AUDIT table.
DOC_SEQUENCE_VALUE NUMBER : Sequence name assigned to an invoice, based on the document category of the invoice. Foreign key to the DOC_SEQUENCE_VALUE of the AP_DOC_SEQUENCE_AUDIT table

This table corresponds to the Invoices header block of Invoice workbench. AP_INVOICES_ALL holds information of all AP invoices whether it is a manually entered, imported, created from other products like Oracle Loans, Oracle Projects, iSupplier Portal, Refunds from Oracle Receivables etc. This table holds all type of invoices, which includes Standard, Prepayments, Credit Memo, Debit Memo, Mixed invoice, Withholding invoice, Interest Invoice, Retainage invoices, Payment Requests etc., An invoice can also have one or more scheduled payments. There will be one row for each invoice you enter.
An invoice can have one or more invoice lines and each line can have one or more invoice distributions.
An invoice of type EXPENSE REPORT must relate to a row in AP_EXPENSE_REPORT_HEADERS_ALL unless the record has been purged from AP_EXPENSE_REPORT_HEADERS_ALL.
Oracle Payables application uses the INTEREST type invoice for interest that it calculates on invoices that are overdue. Oracle Payables application links the interest invoice to the original invoice by inserting the INVOICE_ID in the AP_INVOICE_RELATIONSHIPS table.
The accounting code combinations stored in this table is meta data for creating accounting entries in Subledger Accounting. Payables provides the code combinations stored in this table to Subledger Accounting as a source for accounting attributes for deriving the accounting code combinations. Subledger Accounting generates the final accounting entries that are posted to General Ledger. The accounting code combination used in the final accounting entries can be same as that stored in AP_INVOICES_ALL table or can be different depending on the rules setup in Subledger Accounting. The XLA_AE_HEADERS and XLA_AE_LINES tables in Subledger Accounting stores the accounting entries posted to General Ledger.

AP_HOLDS_ALL